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Method Of Synchronizing Images On Multiple Display Devices With Different Refresh Rates - Patent 7868848


BACKGROUNDA personal computer (PC) system may house one or more graphics subsystems. A graphics subsystem may have one or more display controllers, each of which is attached to a display device such as a VGA monitor or a TV. In the following, a displaycontroller and its attached monitor/TV will generally be referred to as a display device when no ambiguity exists.Microsoft's Windows family operation systems have become the industry's de facto standard. Their methods of displaying images/video have been patented under U.S. Pat. Nos. 5,844,569 and 5,850,232. When displaying a sequence of images, suchas playing DVD, individual images are rendered into image buffers (surface locations), or blocks of video memory, and then the image buffers are displayed sequentially according to a specified timing. This display method is commonly termed as flip,meaning that the image buffer currently on display is replaced by another buffer containing a new image. The replaced image buffer becomes available again for receiving a newer image. In other words, the buffers are swapped.However, the methods described in the referred patents are limited to the case where the image or video is shown on one display device, either in a window of the display or in the full screen. The two display modes will be referred to as thewindow mode and the full screen mode respectively. When a computer system has two display devices, Windows has two methods of showing the image. One is to duplicate the screen of one display to another, commonly referred to as the clone mode, whetherthe image is shown in a window or in a full screen. The other is to show the image on one of the display devices, which is often referred to as the extended desktop mode. A limitation of the clone mode is that the two monitors have to be set toidentical refresh rates.As such, Microsoft's methods are incapable of supporting the application where the user requires one of the displays to be his/her conventional worki

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